June 10, 2012

Assessing Neolithic Europeans with 'weac2'

I have used the West Eurasian cline calculator 'weac2' to assess the TyroleanIceman and NeolithicSwedes. The admixture proportions can be seen below, and appear largely consistent with all previous analyses of the same individuals:

It is interesting that Gok4, the Swedish Megalithic TRB female belongs to the Atlantic_Baltic and Near_East components, while the two major Y-chromosome haplogroups associated with West European Neolithic sites so far are I2a1 and G2a (Treilles and Dolmen of La Pierre Fritte) whose distribution very well parallels these two components: Atlantic_Baltic/I2a1 in Europe, and Near_East/G2a in the Near East.

The simplest explanation, based on the available evidence, is that the Neolithic populations of Europe were descended from G2a-bearing pioneers entering Europe from the southeast, and encountering an I2a1-bearing population of pre-farmers in Europe itself. The high frequency of I2a1 in Sardinia, as well as the presence of G2a in that population serves to underscore the substantial genetic continuity between ancient Neolithic Europeans and modern Sardinians.

The absence of the South_Asian component in 'weac2' in all of these individuals is also important. This component captures ancestry (both Caucasoid and Ancestral South Indian) from further east and south, where both G2a/I2a1 are quite rare. As I have notedbefore, both Europe and South Asia have been affected in late/post-Neolithic times by migrations from West Asia.

It is tempting to associate this population movement with the spread of Indo-European languages, and we can only eagerly await more autosomal ancient DNA samples that will reveal the arrival of the "missing components" over the Neolithic substratum.

A problem with the French study you have used, however, is that it ''assumes'' that I2a is pre-Neolithic, based on the study by Rootsi which used the Zhivotosky method to come up with the hypothesis that Hg I lived in a LGM Balkan refuge. This has not been confirmed by direct aDNA studies. Whatever the age of Hg I, unless we confirm a pre-Neolithic presence in Europe, the possibility that I also arrived in Europe during the Neolithic from the Near East (given its relationship to Hg J) cannot be excluded.

I don't put much emphasis on Y-STR based age estimates anymore, but I believe that even Ken Nordvedt who uses germline rates believes that haplogroup I is Paleolithic in Europe.

This also makes sense of the fact that haplogroup I is so European-specific. I had previously resisted the idea of extreme antiquity of I in Europe on the basis of the idea that it "would have spilled out" over long periods of time, but it increasingly seems that Europe was a population sink rather than a population source during prehistory.

"I don't put much emphasis on Y-STR based age estimates anymore, but I believe that even Ken Nordvedt who uses germline rates believes that haplogroup I is Paleolithic in Europe."

True; and as has been shown by SNP studies, it is probably Palaeolithic in age; however, even though it is European specific "today", it still could have potentially arisen in the Middle East from the ancestral IJ and then later drifted out/ selected out/ bred out.

"but it increasingly seems that Europe was a population sink rather than a population source during prehistory."

I think the general case is population will flow in the direction of military advantage until it reachs a line of equilibrium. Numbers are a military advantage so with all else being equal movement from high pop. density regions to low pop. density regions is a specific case of that general rule. The equilibrium line being where the pop. density is the same either side of the line.

In true then if the initial farming package was limited to a band of latitude then the northen edge of that band would be the line of population density equilibrium. The line might move north gradually as crops were improved but the people north of that line would never be a source unless something changed the balance.

(Like someone sailing along the atlantic coast and introducing cattle behind the equilibrium line turning the low pop. density foragers into medium pop. density herders thereby causing them to expand down over the non-herders to meet the original equilibrium line from the other direction.)

It is interesting to note that Otzi and GOK4 belong to both the Atlantic_Baltic and Near East components while the two hunter-gatherer samples belong completely to the Atlantic_Baltic component. I wonder then if this means that the Atlantic_Baltic component is a mixed Mesolithic/Neolithic component while the Near East component is a more purely Neolithic one?

But Dienekes you have to consider the scenario that Major ANI ASI admixture started to happen only in around 1500b.c. as to the Moorjani et al. And as Metspalu et al. Have suggested the least age of ANI is 12500YBP in South Asia! So its not surprising at all that neolithic DNA is not providing the SA component.P.S. aDNA from Farmana is going to play a crucial role to find the direct truth just like in Europe and others.

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